This invention relates to the construction of ink drop ejector components of printheads used in ink-jet printing.
An ink-jet printer typically includes one or more cartridges that contain ink. In some designs, the cartridge has discrete reservoirs of more than one color of ink. Each reservoir is connected via a conduit to a printhead that is mounted to the body of the cartridge.
The printhead is controlled for ejecting minute drops of ink from the printhead to a printing medium, such as paper, that is advanced through the printer. The printhead is usually scanned across the width of the paper. The paper is advanced, between printhead scans, in a direction parallel to the length of the paper. The ejection of the drops is controlled so that the drops form recognizable images on the paper.
The ink drops are expelled through nozzles that are formed in a plate that covers most of the printhead. The nozzle plate is typically bonded atop an ink barrier layer of the printhead. That barrier layer is shaped to define ink chambers. Each chamber has adjacent to it a nozzle through which the ink drops are expelled.
Ink drops are expelled from an ink chamber by a heat transducer, which typically comprises a thin-film resistor. The resistor is carried on an insulated substrate, such as a conventional silicon die upon which has been grown an insulation layer, such as silicon dioxide. The resistor is covered with suitable passivation and cavitation-protection layers, as is known in the art and described, for example, in U.S. Pat. No. 4,719,477, hereby incorporated by reference.
The resistor has conductive traces attached to it so that the resistor can be selectively driven (heated) with pulses of electrical current. The heat from the resistor is sufficient to form a vapor bubble in an ink chamber, the rapid expansion of which propels a drop through the adjacent nozzle.
The chamber is refilled after each drop ejection with ink that flows into the chamber through a channel that connects with the conduit of reservoir ink. The components of the printhead (such as the heat transducer and ink chamber) for ejecting drops of ink are oftentimes referred to as drop ejectors. The action of ejecting a drop of ink is sometimes referred to as xe2x80x9cfiringxe2x80x9d the resistor or drop ejector. The ink chambers are hereafter referred to as firing chambers.
Print quality is generally improved when one can precisely control the volume of the individual ink drops that are expelled from the printhead. In this regard, it is important to ensure that the drop volume does not uncontrollably change from one drop to the next. Also, as a general rule, the smaller the volume of expelled drops, the higher the print quality.
As noted, the refill ink rapidly flows into the chamber after each printhead firing. This behavior of the refill ink can be characterized as a wave action in which refill ink initially surges into the chamber and then backflows slightly. This cycle is repeated in diminishing magnitude until the ink in the chamber is sufficiently quiescent for firing the next drop. The chamber and channel leading to it are designed to provide passive damping of the refill ink to shorten the time required to reach the quiescent condition.
For high quality printing, it is important that the refill process is damped to an extent that no xe2x80x9covershootingxe2x80x9d or xe2x80x9cundershootingxe2x80x9d occurs. Overshooting occurs when the volume of ink in the firing chamber is greater than a quiescent or steady state volume. Firing at such time causes a relatively larger drop to be ejected. Undershooting occurs when the volume of ink in the firing chamber ebbs below the steady state volume. Firing at such time causes a relatively smaller drop to be ejected. As noted, such uncontrolled changes in drop volume will have deleterious effects on print quality.
In view of the foregoing, it will be appreciated that chamber refill times can be limiting factors as respects the overall printing speed or throughput of the printer. That is, the frequency with which the firing chamber can be refilled and the refill-ink sufficiently damped limits the frequency with which uniform-volume drops can be expelled.
Most printers permit at least two print modes: draft and high-quality. Draft modes sacrifice print quality (by permitting some overshooting, for example) in exchange for faster throughput. A draft mode of printing may allow firing of the printheads at frequencies as much as four times faster than high-quality mode.
Despite the availability of two print modes, the conventional use of a single firing chamber configuration for both modes means that the printhead designer must select a compromise configuration for the firing chamber. That compromise design is one that, while permitting relatively high-frequency draft mode, must still passively dampen (hence, slow) the flow of refill-ink to the firing chamber to allow uniform-volume printing in high-quality mode at a reasonable printing speed.
The present invention frees the designer from the design compromise just mentioned by providing on the same printhead two different firing chamber configurations. One set of firing chambers provides large-volume drops, and rapid refill times to facilitate draft-mode printing. A second set of firing chambers provides smaller drop volumes and more controlled refill rates that are optimized for high-quality printing.
As another aspect of this invention, the two sets of chambers are aligned in a manner that permits high resolution printing in both draft and high-quality mode.
The present invention also permits the nozzle configurations for each firing chamber to be optimized for the print mode that is carried out by that particular firing chamber. Also, the draft-mode-dedicated nozzles require much less intermittent servicing, which is automatically performed by a service station that is installed in the printer. As a result, draft mode operation is less often interrupted for servicing as compared to the high-quality mode operation, which produces better drop configurations but requires more frequent servicing.
Apparatus and methods for carrying out the invention are described in detail below. Other advantages and features of the present invention will become clear upon review of the following portions of this specification and the drawings.